The present invention relates to a frictionless, high-pressure sealing device for sealing a ship's body adjoining the stern tube holding the propeller shaft against invasion of sea water along the propeller shaft.
The conventional means to seal a ship's body adjoining the stern tube of the propeller shaft against invasion of sea water through the propeller shaft are the gland seal, the face type seal and the oil seal.
The gland seal includes packing provided with the propeller housing that externally seals the propeller shaft against sea water. This device is satisfactory in sealing performance but it has the unavoidable drawbacks that some of the power to drive the propeller shaft is lost due to friction caused by tight packing of the propeller shaft, and the shaft sleeve suffers wear from abrasion.
The face type seal includes a seal ring fitted to the periphery of the propeller shaft by means of a garter spring. The end face of the seal ring is circumferentially caused to slide against the inner wall of the housing, thereby yielding a sealing effect. This device has the following disadvantages: Since the seal-ring is positioned by means of a garter spring, it is difficult to secure a high-pressure seal; the seal is rendered useless if an eccentricity develops in the propeller shaft, power is unavoidably lost due to the friction between the seal-ring and the housing, which also suffers wear from an abrasion of the wall of the housing.
The oil seal is a device developed to eliminate the power loss due to friction, which is a common defect to the above-mentioned two devices. This device is designed so that a gap left between the inner wall of the housing and the propeller shaft is supplied with oil which forms a continuous film, thereby yielding a sealing effect. The most serious problems with this device are that, with no external means available to control the oil, oil consumption is heavy and a high-pressure seal is difficult to attain.